Passive and active response of bacteria under mechanical compression.

The ability to maintain a positive turgor pressure, by means of higher osmolarity of the cell interior than the exterior, is a requirement for proper metabolism in walled microbial cells. Turgor pressure is sensitive to changes in external osmotic conditions, and is drastically increased upon osmotic downshock, together with cell volume.
Bacteria prevent lysis caused by excessive osmotic pressure through mechanosensitive (MS) channels: membrane proteins that release solutes (ions) in response to mechanical stress. The exact mechanism of channel gating in the natural setting, however, has been elusive due to the lack of experimental methods appropriate for the small dimensions of prokaryotes.
We here present experimental data on the gating of MS channels of E. coli subjected to compressive force under iso-osmotic conditions. We indent living cells with micron-sized beads attached to the cantilever of an atomic force microscope (AFM) and characterize the mechanical response. We show that turgor pressure can be monitored through the measured response and quantify its value and fluctuations for individual single cells before and after MS channel gating.